142 M. Secchi on Earth Cwrents, and their 



The conclusions, to be drawn from this Table are obviously 

 the following : — 



(1) The fluctuation of the current in the direction of the ver- 

 tical (or equatorial) is greater than in the direction of the meri- 

 dian. 



(2) The maximum of the one corresponds to the minimum 

 of the other, so that the two periods are almost complementary; 

 thus the maximum of the equatorial is about 8 o'clock, and 

 the minimum of the meridian is at 7 o'clock, or 7.30 ; the equa- 

 torial minimum is midday, and the meridional maximum between 

 11 o'clock and midday. I say between these limits, because as 

 the observations were not always made exactly at the hour, in the 

 mean these fractions of an hour were reduced to the nearest 

 entire hour, which is adequate in this matter. 



(3) Besides the principal maxima and minima, there are, 

 after midday, other but more feeble secondary maxima and 

 minima, in which the same law of complement prevails as 

 that observed in the morning. 



(4) During night the current is almost constant, but higher. 

 From the nature of these results, it appeared impossible to 



attribute these currents to thermal actions, from whatever point 

 of view they are regarded. But these results give a valuable 

 clue to the discovery of the source of these variations, and show 

 that it is sufficient to compare the period of the current in one 

 direction to obtain that of the other ; and thus our researches may 

 be utilized although made solely in the direction of the meri- 

 dian. 



The three following Tables condense the observations made 

 during one year in the meridional terrestrial current from Rome 

 to Anzio, and I compare it with those of the bifilar and of atmo- 

 spheric electricity. I do not add the periods of the declino- 

 meter and of the vertical, because they are simpler and better 

 known. The minimum of the vertical is between 11 o'clock 

 and midday ; that of the declinometer according to well-known 

 laws. The maxima of the vertical are the morning and the 

 evening, after which there is a feeble nocturnal minimum. 

 What most affects the bifilar is that its period changes with 

 the season, so that in winter the minimum after midday dis- 

 appears. 



